The liquid crystal display device comprises an array substrate. As illustrated in FIG. 1, each pixel in the array substrate comprises a thin film transistor 2′ and a plate-like pixel electrode 3′ sequentially disposed on a base substrate 1′; the thin film transistor 2′ comprises a gate 21′, a gate insulation layer 22′, an active layer 23′, and a source 24′ and a drain 25′ located in the same layer, herein the gate insulation layer 22′ extends to the region where the pixel electrode 3′ is located; the pixel electrode 3′ is formed on the gate insulation layer 22′, and extends from the gate insulation layer 22′ to the top surface of the drain 25′, so as to overlap the drain 25′.
In the process of manufacturing the array substrate, in order to reduce the number of masks, the array substrate is usually exposed by using a gray-scale mask. The drain 25′ and the drain region of the active layer 23′ corresponds to the completely-light-blocked region of the gray-scale mask, so that the outer edge of the drain 25′ is aligned with the edge of the active layer 23′. At the outer edge of the drain 25′, the step difference between the drain 25′ and the gate insulation layer 22′ is equal to the sum of the thickness of the drain 25′ and the thickness of the active layer 23′. Commonly, the thickness of the drain 25′ is 0.4 μm, the thickness of the active layer 23′ is 0.25 μm, therefore, the step difference is 0.65 μm, which is relatively larger with respect to the thickness of 0.05 μm of the pixel electrode 3′, resulting in that the pixel electrode 3′ is cracked when it is climbed from the gate insulation layer 22′ to the top surface of the drain 25′, thus the display effect of the display device is affected.